Dielectric gases have found increasing use in high voltage systems, especially over about 100 kilovolts, with the most widely used material being sulfur hexafluoride. Sulfur hexafluoride has been used in both devices with uniform fields, such as compressed gas insulative devices, and in devices with non-uniform fields, such as circuit breakers and transformers. The rating of a particular device depends upon its configuration, the gas pressure, the dielectric gas used, the degree of freedom of the gas from moisture and other contamination, and other conditions. Nevertheless, there is a continuing need for dielectric gases of increased dielectric strength under comparable conditions that permit a given device to merit a higher voltage rating or permit alterations in other parameters with the maintenance of a rating.
Various gases, especially electronegative gases, have been proposed as additives to sulfur hexafluoride or alternates for sulfur hexafluoride. Some such gases also contain sulfur while others do not. The proposed substitutes and alternates to sulfur hexafluoride which contain sulfur, have one or more sulfur atoms at valence state 6 or 4 or otherwise bonded with four or six electron pairs. Exemplary in U.S. Pat. No. 3,674,696 (issued July 4, 1972 to Griffiths) wherein compounds are disclosed as dielectric gases with S at valence state 4 such as SN(CF.sub.3)F.sub.2, SN(C.sub.2 F.sub.5)F.sub.2, SN(C.sub.3 F.sub.7)F.sub.2 or S at valence state 6 such as SN(CF.sub.3)OF.sub.2, SN(C.sub.3 F).sub.7 OF.sub.2, S(NCF.sub.3).sub.2 F.sub.2, S(NCF.sub.3)F.sub.2 and S(NC.sub.2 F.sub.5)(NC.sub.3 F.sub.7)F.sub.2. It has hitherto been thought, howver, that sulfur at valence state 2 was too easily oxidized to offer high dielectric strength in a dielectric gas.